It is common for companies to have more than one kind of equipment utilizing hydraulic pumps. For example, trucking companies often have both trucks with dump trailers and trucks with live-floor trailers. A dumping system for a trailer quickly unloads material from the trailer floor by tipping or tilting the trailer floor with a hydraulic drive system so that the material slides off either an end or a side of the floor depending on the direction that it is tipped. A live or moving floor for a trailer moves material along the trailer floor to facilitate loading and unloading. Typically, the floor is divided into three sets of narrow floor slats with every third slat connected together to move forward and backward in unison by operation of hydraulic drive system. When all three sets of slats move in unison in one direction, the material resting thereon moves along with them. Slat retraction (during which the material does not move) is accomplished by moving only one of the sets of slats at a time (friction of the material resting on the two stationary sets of slats keeps the material from moving while the single moving set of slats slides past).
Hydraulic drive systems for dump trailers typically operate at about 2500 PSI pressure and hydraulic drive systems for live floor trailers typically operate at about 3200 PSI pressure. Therefore, trucking companies utilizing both dump trailers and live floor trailers must stock, install, and maintain multiple types of hydraulic pump systems and components such as, for example, pressure relief valves. Pressure relief valves are utilized to protect the hydraulic system from excess pressure by automatically relieving system pressure when the system pressure reaches a predetermined relief pressure which indicates there is some kind of failure within the system before there is a catastrophic failure. Thus, the trucking companies must use different pressure relief valves to account for the differing operating pressures of the dump trailers and the live-floor trailers.
Accordingly, there is a need for an improved relief valve that can be selectively actuated to automatically operate at one of at least two predetermined relief pressures so that it can be utilized in hydraulic pump systems having differing operating pressures such as, for example, hydraulic pump systems of dump trailers and live floor trailers.